This study examines how existing and new policies that affect the generosity of state Medicaid programs impact breast and cervical cancer screening and related health outcomes among low-income women. There are substantial disparities in breast and cervical cancer diagnosis, treatment, and outcomes in the United States by race/ethnicity and socioeconomic and insurance status. Further, resources to improve access to and quality of care for underserved populations are limited. In recent years, the federal government granted many states increased flexibility to cover low-income adults through Medicaid waivers. Further expansions to Medicaid are anticipated under the Patient Protection and Affordable Care Act (ACA). Current variation in state Medicaid programs and anticipated changes under the ACA provide natural experiments for studying the effect of public insurance on screening for low-income women. We consider the effect of pre- and post-reform variation in eligibility between and within states, as well as the effect of physician payment and patient cost sharing on screening. Understanding how state Medicaid policies affect cancer screening will help guide strategies to reach under-screened populations and add to evidence regarding the costs and benefits of different policies. In addition, we study how variation in Medicaid generosity across states and over time is related to outcomes including cancer incidence and stage at diagnosis, the single most important predictor of survival. The project brings together complementary secondary data from a number of sources. Nationally representative survey data from the Behavioral Risk Factor Surveillance System will be used to study the effects of Medicaid eligibility on breast and cervical cancer screening among low-income populations. Medicaid administrative claims and utilization data will allow us to consider the effects of changes in eligibility as well as physician payment and patient cost sharing on screening among Medicaid enrollees. Surveillance, Epidemiology, and End Results (SEER) cancer registry data will be used to estimate the effects of changes in Medicaid generosity on cancer incidence and stage at diagnosis. Our analytic approach employs a quasi- experimental design to compare changes in outcomes among groups that would have been affected by changes in Medicaid policy (eligibility, payment rates, or cost sharing) to similar groups that were not subject to polcy changes. In addition to considering the effect of policy changes on all low-income women, we will examine whether effects of expansions are larger among racial and ethnic minorities, reducing disparities. This is the first study to consider the effect of recent Medicaid policies regarding eligibility, physician payment, and cost sharing on breast and cervical cancer screening, which are the most important measures for the prevention of breast and cervical cancer morbidity and mortality. The results will provide timely evidence on how Medicaid policy affects women's preventive healthcare utilization and health outcomes.